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Biomedical subjects

L G Duckert

Publications and source records attributed to L G Duckert.

45 records · Page 3Linked to original sources
PubMedDate not supplied

Visual impairment and cognitive dysfunction in Alzheimer's disease.

OBJECTIVE: To determine whether impaired visual acuity is associated with dementia and cognitive dysfunction in older adults. DESIGN: Paired case-control comparisons of the relative frequencies of visual impairment in demented cases and nondemented controls. Cohort analyses of correlation between visual acuity and cognitive functioning in demented cases. SETTING: Internal medicine clinics at two academically affiliated medical centers. PARTICIPANTS: Eighty-seven consecutively selected patients greater than or equal to 65 years of age with mild-to-moderate, clinically diagnosed Alzheimer's disease (cases) and 87 nondemented controls matched to the cases by age, sex, and education. MEASUREMENTS AND MAIN RESULTS: The prevalence of visual impairment was higher in cases than in controls [unadjusted odds ratio for near-vision impairment = 2.7 (95% CI = 1.4, 5.2); unadjusted odds ratio for far-vision impairment = 2.1 (95% CI = 1.02, 4.3); odds ratios adjusted for family history of dementia, depression, number of medications, and hearing loss were 2.5 (95% CI = 1.1, 10.5) for near-vision impairment and 1.9 (95% CI = 0.8, 4.6) for far-vision impairment]. When further stratified by quartiles of visual acuity, no statistically significant "dose-response" relationship between vision impairment and dementia risk was observed. Among cases, the degree of visual impairment was significantly correlated with the severity of cognitive dysfunction for both near and far vision (adjusted ps less than 0.001). CONCLUSIONS: Visual impairment is associated with both an increased risk and an increased clinical severity of Alzheimer's disease, but the increased risk may not be consistent with a progressive dose-response relationship. Further studies are needed to determine whether visual impairment unmasks and exacerbates the symptoms of dementia or is a marker of disease severity.

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Validity and reliability of auditory screening tests in demented and non-demented older adults.

The validity and reliability of auditory screening tests were evaluated in 34 demented and 31 non-demented elderly outpatients. In reference to an audiometric gold standard (40-dB HL hearing loss in speech frequencies), 512-Hz and 1024-Hz tuning forks, finger rub, and whispered voice tests performed well (ROC curve areas = 0.82 to 0.94). Simultaneously high (greater than 0.80) sensitivities and specificities were achievable for all these tests in demented patients. In non-demented patients, however, only the whispered voice test achieved simultaneously high specificity and sensitivity. The most accurate rule for air conduction screening audiometry was the inability to hear greater than or equal to two of four 40-dB HL speech frequencies (sensitivity = 1.0, specificity = 0.75 in non-demented patients; sensitivity = 0.97, specificity = 0.74 in demented patients). Interobserver/test-retest reliability was generally high for tuning forks, finger rub, and whispered voice tests (range of intraclass correlation coefficients = 0.38 to 0.90), and was somewhat higher in demented than in non-demented patients. These results suggest that some of the simple, traditional methods of auditory screening may have considerable validity and reliability in demented and non-demented older adults.

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Necrotizing sialometaplasia of the nasopharynx.

Necrotizing sialometaplasia is an uncommon salivary gland disease originally described by Abrams et al in 1973. The disease may occur wherever salivary gland tissue is found. Theories on the etiology of this disorder have been advanced, but never definitely determined. Treatment consists of adequate biopsy and observation until healing occurs at six to eight weeks. While the disease is considered benign, its similarity to more aggressive neoplasms can be both disturbing and misleading to the patient and the clinician. Such a case of necrotizing sialometaplasia of the nasopharynx is presented to demonstrate the clinical and histological similarity of this disease to carcinoma. In this case, the patient first presented with a neck mass which could easily have been mistaken for a regional metastasis. The current literature is reviewed.

Diagnosis, Differential↗
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Acute morphological changes in guinea pig cochlea following electrical stimulation. A preliminary scanning electron microscope study.

A major area of concern in the development of the cochlear prosthesis involves the effects of the implant on inner ear anatomy and function. This study examined one aspect of host-implant interaction- the effects of cochlear implantation with and without electrical stimulation on cochlear morphology in the guinea pig. To accomplish this, a series of normal guinea pigs were acutely implanted bilaterally with a scala tympani multiple electrode prosthesis. One ear was stimulated with continuous 1 kHz sinusoidal current of constant intensity for a period of three hours. The contralateral control ear was not stimulated. Current intensities tested ranged from 0.1 mA to 1 mA rms. After stimulation the animals were sacrificed, perfused with fixative and the temporal bones were microdissected for examination using the scanning electron microscope. Morphological changes observed in the stimulated ear ranged from hair cell and supporting cell degeneration to complete destruction of the basilar membrane and organ of Corti overlying the electrode. These changes occurred at current intensities ranging from 0.4 mA to 1 mA and were conspicuously absent in the implanted but unstimulated control ears. The current intensities employed in this experiment were within operating ranges presently used in long-tern behavioral studies in other animal models. To what degree the morphological changes observed in this study may effect the function of the prosthesis or host responses on a long-term basis cannot be determined from this experiment. However, our observations do demonstrate that electrical stimulation of the cochlea is not benign and point out the need for further evaluation to help define safe standards for use of the prosthesis.

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PubMedDate not supplied

Cochlear prostheses: stimulation-induced damage.

The effects of 4 weekly, three-hour exposures to continuous sinusoidal (l kHz) electrical stimulation of the inner ear at various current levels were assessed in the chronically implanted guinea pig. With scala tympani stimulation, histopathological damage, including new bone growth, was observed for currents at and above 100 microA rms. No changes were observed in similarly implanted, but not stimulated cochleas. At equal current levels, less damage was found in subjects stimulated via electrodes placed on the round window and promontory, as compared to the scala tympani. Consistent reversible changes in threshold and suprathreshold features of the electrically evoked auditory brainstem response (EABR) were found. The magnitude of EABR change was directly related to exposure stimulus current level and to cochlear stimulation site. Suprathreshold features of the EABR were more sensitive to continuous stimulation exposures than threshold measures. Reversible EABR changes were found in the presence and absence of stimulation-induced histopathology.

Animals↗
PubMedDate not supplied

Mechanisms of electrically induced damage after cochlear implantation.

This report is the fourth in a series of parametric studies designed to evaluate and define conditions that may produce histological damage by means of electrical stimulation from cochlear prostheses. Earlier studies established damage thresholds for both acute (400 microA rms or 70 microC/cm(2)0) and chronic (100 microA rms or 15 to 20 microC/cm(2)0) stimulation with continuous sinusoidal current of 1,000 Hz. In a subsequent study, a tenfold reduction in the stimulation frequency (to 100 Hz) resulted in a 50% reduction in the acute damage threshold (200 microA rms), which was a smaller reduction than anticipated if damage is dependent only on charge density. This finding and the damage patterns observed in the preceding studies suggested that multiple mechanisms are responsible for the sensory and supporting cell degeneration induced by the electrical stimulus. A similar pattern of structural changes has been observed by other investigators after acoustic stimulation of the cochlea, suggesting that common mechanisms may be involved. With electrical stimulation, electrophoretic effects have been implicated; like acoustic trauma, however, mechanical, biochemical, and metabolic processes may also be involved. This investigation was designed to identify and analyze better the damage mechanisms active in acute stimulation. Sixteen normal guinea pigs were implanted and stimulated using an interrupted 1,000-Hz signal at 500 microA for three hours. Duty cycle was reduced to 50% and signal periodicity ranged from 100 to 1,000 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Cochlear communication routes in the guinea pig--spiral ganglia and osseous spiral laminae: an electron microscope study using microsphere tracers.

The microscopic and ultrastructural anatomy of the spiral ganglia and osseous spiral laminae (OSL) of the guinea pig were studied using the transmission and scanning electron microscopes. The nerve and vascular elements within the spiral ganglia and OSL are surrounded by distinct perineural and perivascular spaces maintained by a loose meshwork of cells and connective tissue fibers. The connective tissue cells are fibers within the OSL and spiral ganglia are distinctly different from the arachnoid-like reticular cells and elastin fibers of the modiolus described in an earlier study. The present experiment demonstrates a pathway between the perineural spaces of the modiolus, spiral ganglia, and OSL. The perineural spaces of the modiolus were previously shown to communicate with the subarachnoid space; therefore, perineural communication from the cerebrospinal fluid to the perilymph via this route is likely. Using mircosphere tracers injected intrathecally, this communication route between the subarachnoid space and scala tympani was further defined. The tracer experiment suggests that the perineural spaces within the internal acoustic meatus, modiolus, spiral ganglia, and OSL are normally patent and do not represent artifacts induced during tissue processing.

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